U.S. patent application number 14/429890 was filed with the patent office on 2015-08-13 for formulations containing conductive polymers and use thereof in organic electronic devices.
This patent application is currently assigned to Merck Patent GmbH. The applicant listed for this patent is MERCK PATENT GMBH. Invention is credited to Heinrich Becker, Susanne Heun.
Application Number | 20150228902 14/429890 |
Document ID | / |
Family ID | 47010149 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150228902 |
Kind Code |
A1 |
Becker; Heinrich ; et
al. |
August 13, 2015 |
FORMULATIONS CONTAINING CONDUCTIVE POLYMERS AND USE THEREOF IN
ORGANIC ELECTRONIC DEVICES
Abstract
The invention relates to formulations containing doped
conductive polymers, which due to outstanding hole injection
characteristics and high conductivity are very suitable for use in
organic electronic devices, preferably in organic
electroluminescent devices, in particular in the buffer layers
thereof. Thus the invention further relates to the use of the
formulations according to the invention in organic electronic
devices, preferably in electroluminescent devices, in particular in
the buffer layers thereof.
Inventors: |
Becker; Heinrich;
(Ober-Ramstadt, DE) ; Heun; Susanne; (Bad Soden,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MERCK PATENT GMBH |
Darmstadt |
|
DE |
|
|
Assignee: |
Merck Patent GmbH
Darmstadt
DE
|
Family ID: |
47010149 |
Appl. No.: |
14/429890 |
Filed: |
September 5, 2013 |
PCT Filed: |
September 5, 2013 |
PCT NO: |
PCT/EP2013/002673 |
371 Date: |
March 20, 2015 |
Current U.S.
Class: |
252/519.2 ;
252/500 |
Current CPC
Class: |
H01L 51/0035 20130101;
C08G 2261/1424 20130101; C08L 65/00 20130101; C08G 2261/512
20130101; H01L 51/0037 20130101; H01L 51/5016 20130101; C08G
73/0611 20130101; C08G 73/0266 20130101; H01L 51/5088 20130101;
C08G 61/126 20130101; C08L 25/18 20130101; C08G 2261/95 20130101;
H01L 51/506 20130101; C08L 79/02 20130101; C08G 2261/794 20130101;
C08L 65/00 20130101; C08L 79/04 20130101 |
International
Class: |
H01L 51/00 20060101
H01L051/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2012 |
EP |
12006695.6 |
Claims
1.-10. (canceled)
11. A formulation comprising at least one doped, conductive
polymer, at least one oxidant and at least one solvent.
12. The formulation according to claim 11, wherein the conductive
polymer is a polythiophene, a polythiophene derivative, a
polyaniline, a polyaniline derivative, a polypyrrole or an
oligoaniline.
13. The formulation according to claim 11, wherein the content of
the at least one doped, conductive polymer in the formulation is in
the range from 0.001 to 30% by weight.
14. The formulation according to claim 11, wherein at least one
oxidant is selected from the group consisting of organic and
inorganic peroxides, peracids, persulfates, perborates, metal
salts, derivatives of halogen oxyacid, nitrates, halogens, ozone,
nitrogen oxides, nitroso compounds, and oxygen.
15. The formulation according to claim 14, wherein the content of
the at least one oxidant in the formulation is in the range from
0.001 to 5% by weight.
16. The formulation according to claim 11, wherein the weight ratio
of doped, conductive polymer to oxidant in the formulation is in
the range from 1000:1 to 1:10.
17. The formulation according to claim 11, wherein the at least one
solvent is selected from the group consisting of water, alcohols,
alkanes, cycloalkanes, alkenes, alkynes, ethers, esters,
halogenated hydrocarbons, aromatic compounds, lactones, carbonates,
sulfoxides, nitro compounds, nitriles, ketones, carboxamides or
urea derivatives, and mixtures of these solvents.
18. The formulation according to claim 17, wherein the content of
the at least one solvent in the formulation is in the range from 65
to 99.99% by weight.
19. A method comprising utilizing the formulation according to
claim 11 in organic, electronic devices.
20. The method according to claim 19, wherein the organic,
electronic device is an electroluminescent device.
Description
[0001] The present invention relates to formulations comprising
doped, conductive polymers which, owing to their excellent
hole-injection properties and their high conductivities, are very
suitable for use in organic, electronic devices, preferably in
electroluminescent devices, in particular in buffer layers thereof.
The present invention thus also relates to the use of the
formulations according to the invention in organic, electronic
devices, preferably in electroluminescent devices, in particular in
buffer layers thereof. Thus, the conductive polymers exhibit
excellent properties as buffer layer in photo-voltaics,
phototherapy and sensor technology. The polymers have a broad
spectral window and good film-formation properties. The materials
are usually processed as aqueous dispersion, but it is likewise
possible to process the materials as solution from organic solvents
or water.
[0002] Doped conductive polymers are known and have long been used
in corrosion protection, in antistatics, in printed electronics and
in organic electroluminescent devices. Their use in OLEDs (organic
light emitting diodes) and PLEDs (polymeric light emitting diodes)
has particular importance.
[0003] The conductive polymers employed are usually polyanilines,
polyaniline/indium complexes, polythiophenes, polythienothiophenes,
polypyrroles and oligoanilines. These may be doped by Bronstedt
acids (polymeric acids, monomeric acids, and by covalently bonded
acid groups).
[0004] The best-known doped conductive polymers include
poly(3,4-ethylenedioxythiophene) (PEDOT) and polyaniline
(PANI).
[0005] Dispersions of poly(3,4-ethylenedioxythiophene) (PEDOT)
which are doped, inter alia, with polymeric sulfonic acids are
disclosed, for example, in EP 0593111 A1. Commercial, aqueous PEDOT
dispersions are obtainable, for example, from Heraeus under the
trade name Clevios and from Agfa-Gevaert under the trade name
Orgacon.
[0006] Dispersions of polyaniline (PANI) and a polymeric sulfonic
acid to which indium has been added are disclosed, for example, in
WO 2007/020100. This document furthermore describes polypyrroles
and polythiophenes (PEDOT derivatives) with added indium. This
document likewise describes dispersions of these materials and the
use thereof in OLEDs. However, the opto-electronic capability and
in particular the optical transparency of the material systems
described are not discussed.
[0007] Furthermore, conductive polythieno[3,4-b]thiophenes,
polythieno[3,2-b]thiophenes and polypyrroles are known for OLED
applications. These are described, for example, in WO 2010/141129.
Furthermore, the use of fluorinated organic Bronstedt acids is
known, as disclosed, for example, in WO 04/029128 and WO 04/029133.
Furthermore, oligoanilines are disclosed, for example, in EP
2062870 and in EP 1773102.
[0008] According to the prior art, the buffer layers used are
suitable for conducting the electrical current, injecting holes and
compensating for unevenness in thin-film electronic applications,
in particular in OLEDs. However, the materials currently frequently
only exhibit inadequate optical transparency and therefore result
in unacceptably large efficiency losses due to light
absorption.
[0009] Surprisingly, it has now been found that the optical
properties of these conductive polymers can be improved while
retaining the other functionality if an oxidant is additionally
added to these materials after the preparation of solution or
dispersion.
[0010] The present application thus relates to a formulation
comprising at least one doped, conductive polymer, at least one
oxidant and at least one solvent.
[0011] The formulation according to the invention preferably
comprises a doped, conductive polymer.
[0012] The doped, conductive polymer employed can be all polymers
which are known to the person skilled in the art for the said
application and are suitable.
[0013] Preferred conductive polymers are polythiophenes, such as,
for example, poly(3,4-ethylenedioxythiophene), and polythiophene
derivatives, such as, for example, polythienothiophenes,
polyanilines and polyaniline derivatives, such as, for example,
polyaniline/indium complexes, polypyrroles and oligoanilines. These
may be doped by Bronstedt acids (inorganic and organic acids,
polymeric acids, monomeric acids, and by covalently bonded acid
groups). Particular preference is given to
poly(3,4-ethylenedioxythiophene) and polyaniline which are doped by
addition of polysulfonic acids.
[0014] The content of the at least one doped, conductive polymer in
the formulation is preferably in the range from 0.001 to 30% by
weight, particularly preferably in the range from 0.01 to 15% by
weight and very particularly preferably in the range from 0.1 to 6%
by weight.
[0015] The formulation according to the invention preferably
comprises an oxidant.
[0016] The oxidant employed can be all oxidants known to the person
skilled in the art.
[0017] Preferred oxidants are organic and inorganic peroxides (for
example hydrogen peroxide and t-butyl hydroperoxide), peracids (for
example m-chloroperoxobenzoic acid and peracetic acid), persulfates
(for example peroxodisulfate and persulfate), perborates, metal
salts (for example potassium permanganate, potassium
hexacyanoferrate(III), iron(III) chloride and chromates),
derivatives of halogen oxyacid (for example perchlorates,
hypochlorites, bromates and periodates), nitrates, halogens (for
example chlorine, bromine, fluorine and iodine), ozone, nitrogen
oxides, nitroso compounds and oxygen.
[0018] The content of oxidant in the formulation is preferably in
the range from 0.001 to 5% by weight, particularly preferably in
the range from 0.05 to 2% by weight and very particularly
preferably in the range from 0.01 to 1% by weight.
[0019] The weight ratio of doped, conductive polymer to oxidant in
the formulation is preferably in the range from 1000:1 to 1:10,
particularly preferably in the range from 500:1 to 1:5 and very
particularly preferably in the range from 100:1 to 1:1.
[0020] In a further embodiment, the oxidant is added in the form of
a gas, which is no longer present in the final formulation.
[0021] The formulation according to the invention preferably
comprises a solvent.
[0022] The solvent employed can likewise be all solvents which are
known to the person skilled in the art and are suitable for the
conductive polymers. A solvent in the present application is taken
to mean not only those in which all components of the formulation
are soluble, but also those in which one or more components of the
formulation are insoluble or not fully soluble, so that the
formulation is, for example, in the form of a dispersion.
[0023] Preferred solvents are: water, alcohols (for example
methanol, ethanol, isopropanol, t-butanol and cyclohexanol),
alkanes (for example heptane), cycloalkanes (for example
cyclohexane), alkenes (for example 1-heptene), alkynes, ethers (for
example diethyl ether, t-butyl methyl ether and tetra-hydrofuran),
esters (for example methyl benzoate), halogenated hydrocarbons (for
example dichloromethane and trichloromethane), aromatic compounds
(for example toluene, anisole, methylanisole, chlorobenzene,
methylnaphthalene and tetralin), lactones (for example
4-butyrolactone), carbonates (for example ethylene carbonate),
sulfoxides (for example dimethyl sulfoxide), nitro compounds (for
example nitromethane), nitriles (for example acetonitrile), ketones
(for example acetone and butanone), carboxamides (for example
dimethylformamide) and urea derivatives (for example
1,3-dimethyl-2-imidazolidone). It is likewise possible to employ
mixtures of these solvents. However, the solvent is particularly
preferably water.
[0024] The content of solvent in the formulation is preferably in
the range from 65 to 99.99% by weight, particularly preferably in
the range from 83 to 99.9% by weight and very particularly
preferably in the range from 93 to 99% by weight.
[0025] The formulations according to the invention can be obtained,
for example, by dissolving or dispersing the doped, conductive
polymer in the at least one solvent and adding the oxidant to the
solution or dispersion or (in the case of gases) introducing the
oxidant by passing through.
[0026] In a further embodiment, the oxidation can also be carried
out electro-chemically.
[0027] In addition, the formulations according to the invention are
used in organic, electronic devices. The present application thus
also relates to the use of the formulations according to the
invention in organic, electronic devices.
[0028] The organic, electronic device is preferably an organic
electroluminescent device (OLED), a polymeric electroluminescent
device (PLED), an organic integrated circuit (O-IC), an organic
field-effect transistor (O-FET), an organic thin-film transistor
(O-TFT), an organic, light-emitting transistor (O-LET), an organic
solar cell (O-SC), an organic, optical detector, an organic
photoreceptor, an organic field-quench device (O-FQD), an organic,
light-emitting electrochemical cell (OLEC) or an organic laser
diode (O-laser).
[0029] It is preferred in accordance with the invention for the
doped conductive polymer to be in the form of a layer (or in a
layer) in the electronic device. The layer thickness here is
preferably in the range from 1 to 1000 nm, particularly preferably
in the range from 5 to 500 nm and very particularly preferably in
the range from 10 to 200 nm.
[0030] The layer can be obtained, for example, by applying the
formulation according to the invention as dispersion or solution
and subsequently removing the at least one solvent.
[0031] The solution can be applied here by all methods which are
known to the person skilled in the art and are suitable for this
purpose. However, the application is preferably carried out by spin
coating or by means of any desired printing process, such as, for
example, screen printing, flexographic printing or offset printing,
but particularly preferably LITI (light induced thermal imaging,
thermal transfer printing) or ink-jet printing. Preference is
likewise given to continuous coating methods, such as, for example,
knife coating, dip coating, roll-to-roll processes and coating by
atomisation technique (airbrush).
[0032] The removal of the solvent can also be carried out by all
methods known to the person skilled in the art. However, the
solvent is preferably removed at elevated temperature and/or under
reduced pressure. The drying by means of (N)IR treatment, as
disclosed, for example, in WO 03/038923 A1, can also be inexpensive
and time-saving, especially in production.
[0033] In general, the layers are dried at temperatures in the
range from 20.degree. C. to 300.degree. C., preferably in the range
from 80.degree. C. to 250.degree. C., particularly preferably in
the range from 100.degree. C. to 240.degree. C. and very
particularly preferably in the range from 140.degree. C. to
220.degree. C. The drying here is preferably carried out at
atmospheric pressure (1013 mbar). However, it is also possible to
carry out the drying under reduced pressure. The heat-drying times
here are preferably greater than 2 minutes, particularly preferably
in the range from 3 minutes to 1 hour and very particularly
preferably in the range from 5 minutes to 20 minutes.
[0034] The layer obtained from the formulation according to the
invention is preferably employed as buffer layer and/or
hole-injection layer in electroluminescent devices, preferably
organic electroluminescent devices (OLEDs) or polymeric
electroluminescent devices (PLEDs).
[0035] It has been found here that the use of the formulation
according to the invention widens the spectral window of optical
transmissivity, but that the other parameters, such as, for
example, hole-injection properties, wetting properties,
conductivity, viscosity, viscoelastic behavior and pH of the
materials, do not change adversely. In particular, the absorption
at the long-wave end of the visual spectrum is significantly less.
The layers produced exhibit increased transparency, while the other
properties, such as, for example, thickness, mechanical hardness,
work function and surface roughness, remain comparable.
[0036] The properties in opto-electronic thin-film applications
profit from the widened optical window. This applies, in
particular, to organic light-emitting diodes and organic solar
cells. In particular, organic light-emitting diodes exhibit higher
efficiency in the red spectral region at the same time as a good
lifetime. Particularly in the case of multilayered devices and/or
white light-emitting diodes, the larger spectral range is of
advantage, since none of the colouring, spectral components is
filtered out selectively. This is particularly important if the
efficiency is to be increased for lighting units by various methods
for improving the coupling-out of light. The emitted photons pass
through the individual layers of the components multiple times
here, which, in the case of red absorption of the buffer layer,
results in selective loss of the red, spectral component.
[0037] The following examples are intended to explain the invention
without limiting it. In particular, the features, properties and
advantages described therein of the defined compounds on which the
relevant example is based can also be applied to other compounds
which are not described in detail, but fall within the scope of
protection of the claims, unless stated otherwise elsewhere.
WORKING EXAMPLES
[0038] The following syntheses are carried out, unless indicated
otherwise, in 3-necked round-bottomed flasks in air. The starting
materials are, unless mentioned otherwise, purchased from ALDRICH
or ABCR.
Example 1
Oxidation of Polyaniline Dispersions
1a) Using Hydrogen Peroxide
[0039] 0.42 ml of a 30% hydrogen peroxide solution in water is
added to 150 ml of a vigorously stirred dispersion of
polyaniline-polystyrenesulfonic acid/indium complex (PANI-In-PSSH)
(4% in water, the preparation is carried out analogously to WO
2007/020100, Example 7), and the mixture is stirred at 60.degree.
C. for 1 hour.
[0040] Viscosity: 3.18 mPas at 40 1/s; pH=1.55
1b) Using Hydrogen Peroxide
[0041] Analogously to Example 1a, 0.85 ml of a 30% hydrogen
peroxide solution in water is added to 150 ml of a vigorously
stirred dispersion of polyaniline-polystyrenesulfonic acid/indium
complex (PANI-In-PSSH), and the mixture is stirred at 60.degree. C.
for 1 hour.
[0042] Viscosity: 2.98 mPas at 40 1/s; pH=1.39
1c) Using Potassium Permanganate
[0043] Analogously to Example 1a, 1.27 g (8 mmol) of potassium
permanganate are added to 150 ml of a vigorously stirred dispersion
of polyaniline-polystyrenesulfonic acid/indium complex
(PANI-In-PSSH), and the mixture is stirred at 60.degree. C. for 1
hour. The dispersion is filtered through a 0.5 .mu.m filter.
[0044] Viscosity: 3.01 mPas at 40 1/s; pH=1.52
1d) Using Potassium Peroxodisulfate
[0045] Analogously to Example 1a, 2.16 g (4 mmol) of potassium
peroxodisulfate are added to 150 ml of a vigorously stirred
dispersion of polyaniline-polystyrenesulfonic acid/indium complex
(PANI-In-PSSH), and the mixture is stirred at 60.degree. C. for 1
hour.
[0046] Viscosity: 2.90 mPas at 40 1/s; pH=1.51
1e) Using Peracetic Acid
[0047] Analogously to Example 1a, 1.33 ml (8 mmol) of 32% peracetic
acid (in acetic acid) are added to 150 ml of a vigorously stirred
dispersion of polyaniline-polystyrenesulfonic acid/indium complex
(PANI-In-PSSH), and the mixture is stirred at 60.degree. 0 for 1
hour.
[0048] Viscosity: 3.21 mPas at 40 1/s; pH=1.74
1f) Using Sodium Hypochlorite
[0049] Analogously to Example 1a, 5.9 ml (8 mmol) of 10% sodium
hypochlorite solution (in water) are added to 150 ml of a
vigorously stirred dispersion of polyaniline-polystyrenesulfonic
acid/indium complex (PANI-In-PSSH), and the mixture is stirred at
60.degree. C. for 1 hour.
[0050] Viscosity: 2.88 mPas at 40 1/s; pH=1.39
1g) Using Ozone
[0051] Ozone (.about.10 g of O.sub.3) is passed through 150 ml of a
vigorously stirred dispersion of polyaniline-polystyrenesulfonic
acid/indium complex (PANI-In-PSSH) by means of an ozone generator
(Innovatec-CMG 10-4) for one hour.
[0052] In order to remove the excess ozone, the mixture is flushed
with nitrogen for one hour.
[0053] Viscosity: 3.21 mPas at 40 1/s; pH=1.29
Example 2
Oxidation of poly(3,4-ethylenedioxy)thiophene polystyrenesulfonate
(PEDOT-PSSH)
2a) Using Hydrogen Peroxide
[0054] 0.1 ml of a 30% hydrogen peroxide solution in water is added
to 100 ml of a vigorously stirred dispersion of PEDOT-PSSH (1.7% in
water, PEDOT/PSSH 1/6, the material is purchased from H. C. Starck
under the name Clevios A14083), and the mixture is stirred at
60.degree. C. for 1 hour.
[0055] Viscosity: 7.18 mPas at 40 1/s; pH=2.03
Example 3
Oxidation of phenyltetraaniline-5-sulfosalicylic acid
[0056] 3a) Using t-Butyl Hydroperoxide
[0057] This reaction is carried out under a blanket of N.sub.2.
[0058] 2.9 ml of a 5.5 M tert-butyl hydroperoxide solution in
decane are added to 100 ml of a vigorously stirred solution of
phenyltetraaniline-5-sulfosalicylic acid (5% in
1,3-dimethyl-2-imidazolidone/cyclohexanol mixture 1:1, preparation
see EP 1773102, Example 1), and the mixture is stirred at
60.degree. C. for 1 hour.
[0059] Viscosity: 1.28 mPas at 40 1/s; pH=3.32
USE EXAMPLES
[0060] Solution-processed OLEDs generally have a simpler structure
than devices produced in vacuo. The latter comprise a multiplicity
of layers having different functions. The individual layers are
applied one on top of the other by vapour deposition, where the
first layer, which is applied to the anode (generally ITO), is
frequently a hole-injection layer ("HIL"). FIG. 1 depicts the
structure of a typical OLED processed from solution, which
comprises few layers. The production of such components is based on
the production of polymeric light-emitting diodes (PLEDs), which
has already been described multiple times in the literature (for
example in WO 2004/037887 A2). Here too, the first layer, which is
deposited on the anode, is a hole-injection layer, which is
frequently also known as buffer layer. The materials according to
the invention can be employed in devices of both types.
Comparative Example V1
[0061] A layer of polyaniline-polystyrenesulfonic acid/indium
complex (4% in water, the preparation is carried out analogously to
WO 2007/020100, Example 7) with a thickness of 80 nm is deposited
on a glass support with the aid of a spin coater at a spin rate of
2530 rpm and dried by heating at 180.degree. C. for 10 minutes. The
film is subsequently protected against water (argon transport box).
The measured absorption spectrum is depicted in FIG. 3.
Example E1
[0062] A film according to the invention of the dispersion from
Example 1a is deposited on a glass support in the same manner as in
Comparative Example V1. The spin rate required for 80 nm is 2300
rpm. The film is likewise dried by heating at 180.degree. C. for 10
minutes and protected against water. The measured absorption
spectrum is depicted in FIG. 3. The absorption in the red spectral
region is significantly reduced.
Comparative Example V2
[0063] In the device configuration of FIG. 1, which is typical of
solution-processed devices, firstly an interlayer, in this case
HIL-012 (0.5% from toluene) (Merck KGaA), is applied to the buffer
layer, which has been deposited analogously to Comparative Example
V1. The spin rate required for a 20 nm interlayer is 2440 rpm, the
interlayer film is dried by heating at 180.degree. C. under a
protective-gas atmosphere for one hour after the spin coating.
Example E2
[0064] On use of the dispersion according to the invention from
Example 1a, the spin rate for the interlayer (HIL-012) is 2380 rpm,
i.e. it is thus virtually identical to the spin rate for
Comparative Example V2. This means that the surface tension and
thus the wettability of the film is also not changed measurably by
the use of the dispersions according to the invention.
Examples E3 to E5, V3
Production of Solution-Processed OLEDs
[0065] Solution-processed OLEDs can be produced using the
formulations according to the invention in the device structure of
FIG. 1 both with and without interlayer. The interlayer material
used in each case is HIL-012 from Merck. The emission layer ("EML",
see FIG. 1) is in both cases a layer with a thickness of 80 nm
applied by spin coating. The materials used in the emission layer
are a green triplet emitter T1 in a matrix of components M1 and M2.
The solvent is chlorobenzene, the proportions of the individual
materials are 20% by weight of T1, 40% by weight of M1 and 40% by
weight of M2.
Structure of Emitter T1:
##STR00001##
[0066] Structure of Matrix M1:
##STR00002##
[0067] Structure of Matrix M2:
##STR00003##
[0068] Example E3
OLED in Device Structure of FIG. 1 (with Interlayer)
[0069] The spin rate required for an 80 nm EML layer on HIL-012 is
1010 rpm. In order to obtain a qualitatively high-quality film, the
solution is warmed to 60.degree. C. and applied by spin coating at
this temperature. After the spin coating, the film is dried by
heating at 180.degree. C. on a hotplate for 10 minutes under
protective-gas atmosphere. 3 nm of barium and 150 nm of aluminium
are applied by vapour deposition as cathode. The devices
encapsulated after the sample production are characterised using a
measurement set-up as depicted in FIG. 2. In addition, an
electroluminescence spectrum is measured at 1000 cd/m.sup.2, from
which the colour coordinates are derived (CIE: Commission
Internationale de I'Eclairage, 1931 standard observer). The
lifetime ("LT") of the devices is likewise measured, where the
lifetime of the device is taken to mean the time after which the
initial luminous density (in this case 1000 cd/m.sup.2) has dropped
to 50%. The results in Table 1 show that the dispersion of Example
1b according to the invention, in spite of the simple device
structure, results in very good triplet green devices.
TABLE-US-00001 TABLE 1 Device results for E3 Max. Max. U @ LT @
eff. EQE 1000 CIE 1000 cd/m.sup.2 Ex. [cd/A] [%] cd/m.sup.2 [V]
[x/y] [hrs] E3 26.1 7.3 6.7 0.34/0.62 6500
Examples V3, V4, E4 to E6
OLEDs in Device Structure of FIG. 1 (without Interlayer)
[0070] Even less expensive and more robust to produce is a device
structure as in FIG. 1, in which the interlayer is omitted. If the
EML is applied directly to the PANI-In-PSSH layer also used for
Comparative Example V1, a very simple green OLED (Comparative
Device Example V3) is obtained. As a further comparative example,
PEDOT can additionally be used as buffer material (Comparative
Device Example V4). The latter is likewise purchased as an aqueous
dispersion from Heraeus (Clevios P 4083 Al) and is processed and
dried by heating analogously to the PANI dispersion (spin rate for
80 nm: 4500 rpm). For comparison, devices comprising buffer layers
1a, 1b and 1f according to the invention are constructed (Examples
E4, E5 and E6). The results are summarised in Table 2. The spin
rates of the EML on the buffer layer are all very close together,
which in turn shows that the adhesion of the EML to the layers
according to the invention is just as good as to the PEDOT which is
widespread in industry. The lifetime ("LT") of the devices is
likewise measured, where the lifetime of the device is taken to
mean the time after which the initial luminous density (in this
case 1000 cd/m.sup.2) has dropped to 50%.
TABLE-US-00002 TABLE 2 Device results for V3, V4, E4, E5 and E6
Spin rate Max. Max. U @ LT @ of EML eff. EQE 1000 CIE 1000
cd/m.sup.2 Ex. [rpm] [cd/A] [%] cd/m.sup.2 [V] [x/y] [hrs] V3 1010
16.7 4.7 7.0 0.34/0.62 1600 V4 1200 22.5 6.2 6.5 0.33/0.62 1300 E4
1210 21.8 6.0 6.2 0.34/0.62 2300 E5 1210 29.7 8.2 6.6 0.34/0.62
5600 E6 1210 21.4 5.7 7.1 0.34/0.62 2500
[0071] As can be seen from the results of Table 2, the use of
formulations 1a, 1b and 1f according to the invention in devices E4
to E6 in all cases results in a significant improvement compared
with the prior art, device V3. In spite of the omission of the
interlayer, the lifetime of device E5 is virtually the same as that
of device E3, the efficiency is even improved again in
comparison.
Comparison of EL Spectra of White Devices on V1 and E1:
[0072] If the transmission of the films [T=10.sup.(-E)] is
calculated from the absorption spectrum in FIG. 3 and the number of
photons absorbed by the film [(1-T)-100] resulting therefrom is
subsequently calculated, it becomes clear how great the difference
and thus the influence on the spectral window is for the films
produced from the formulations according to the invention compared
with the prior art (see FIG. 4). Whereas the film from V1 absorbs,
for example, 20% of all photons at 780 nm, this is only 15% in the
case of the film from E1. For rich-red devices having an emission
wavelength of 625 nm, V1 absorbs about 7.2%, but E1 only about
3.9%. Table 3 shows the proportion of absorbed photons for various
selected wavelengths.
TABLE-US-00003 TABLE 3 Wavelength V1 E1 440 nm 6.48% 6.50% 500 nm
1.48% 1.68% 550 nm 2.88% 2.09% 580 nm 4.23% 2.57% 625 nm 7.19%
3.87%
[0073] In particular, the high absorption in the yellow-red region
is of crucial importance for use of the layers in devices for
lighting applications, where it is desired to construct so-called
"warm-white" lighting elements with a high orange content. The
general problem arises here that the red emission usually exhibits
lower efficiencies, especially compared with green, and in
addition, in order to be able to compete with existing lighting
technology (incandescent bulbs, energy-saving lamps, LEDs) in
respect of energy consumption, use is often made of coupling-out
optics in which the layer may be passed through multiple times.
FIG. 5 shows the EL spectrum of an SPW-111 device (a white OLED
polymer obtainable from Merck) as would change after one, three and
five passages through the V1 or E1 layer. To this end, an EL
spectrum of a standard SPW-111 device (processed from solution, as
described in WO 2004/037887 A2) standardised to 1 was in each case
multiplied by the transmission of V1 or E1 for the number of
passages. Apart from the general loss of efficiency, the colour
shift for the buffer layer in accordance with the prior art V1 is
striking, the red content in the spectrum drops massively. The same
is of course also the case in the much simpler case of a thicker
buffer layer, as is readily employed in large-scale industrial
processes for reasons of production yield. Layer thicknesses of 200
to 250 nm are typical here, which corresponds arithmetically
approximately to the spectra for 3 passages (dotted spectra). Here
too, the colour change and the loss of the red content should
already be clearly noted.
* * * * *